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Launching an EC2 Fleet

An EC2 Fleet contains the configuration information to
launch a fleet—or group—of instances. In a single API call, a fleet can launch
multiple instance types across multiple Availability Zones, using the On-Demand
Instance, Reserved Instance, and Spot Instance
purchasing options together. Using EC2 Fleet, you can:

Specify how Amazon EC2 should distribute your fleet capacity within each purchasing
option

You can also set a maximum amount per hour that you’re willing to pay for your fleet,
and
EC2 Fleet launches instances until it reaches the maximum amount. When the maximum
amount you're
willing to pay is reached, the fleet stops launching instances even if it hasn’t
met the
target capacity.

The EC2 Fleet attempts to launch the number of instances that are required to meet
the target
capacity specified in your request. If you specified a total maximum price per hour,
it
fulfills the capacity until it reaches the maximum amount that you’re willing to
pay. The
fleet can also attempt to maintain its target Spot capacity if your Spot Instances
are interrupted.
For more information, see How Spot Instances Work.

You can specify an unlimited number of instance types per EC2 Fleet. Those instance
types can
be provisioned using both On-Demand and Spot purchasing options. You can also specify
multiple Availability Zones, specify different maximum Spot prices for each instance,
and
choose additional Spot options for each fleet. Amazon EC2 uses the specified options
to provision
capacity when the fleet launches.

While the fleet is running, if Amazon EC2 reclaims a Spot Instance because of a price
increase or
instance failure, EC2 Fleet can try to replace the instances with any of the instance
types that
you specify. This makes it easier to regain capacity during a spike in Spot pricing.
You can
develop a flexible and elastic resourcing strategy for each fleet. For example,
within
specific fleets, your primary capacity can be On-Demand supplemented with less-expensive
Spot capacity if available.

If you have Reserved Instances and you specify On-Demand Instances in your fleet,
EC2 Fleet uses your Reserved Instances. For example,
if your fleet specifies an On-Demand Instance as c4.large, and you have Reserved Instances for
c4.large, you receive the Reserved Instance pricing.

There is no additional charge for using EC2 Fleet. You pay only for the EC2 instances
that the
fleet launches for you.

EC2 Fleet Limitations

An EC2 Fleet request can't span AWS Regions. You need to create a separate EC2 Fleet
for
each Region.

An EC2 Fleet request can't span different subnets from the same Availability
Zone.

EC2 Fleet Limits

The usual Amazon EC2 limits apply to instances launched by an EC2 Fleet, such as Spot
request
price limits, instance limits, and volume limits. In addition, the following limits
apply:

The number of active EC2 Fleets per AWS Region: 1,000 * †

The number of launch specifications per fleet: 50 †

The size of the user data in a launch specification: 16 KB †

The target capacity per EC2 Fleet: 10,000

The target capacity across all EC2 Fleets in a Region: 100,000 *

If you need more than the default limits for target capacity, complete the AWS Support
Center Create
case form to request a limit increase. For Limit type,
choose EC2 Fleet, choose a Region, and then choose Target
Fleet Capacity per Fleet (in units) or Target Fleet Capacity
per Region (in units), or both.

* These limits apply to both your EC2 Fleets and your Spot Fleets.

† These are hard limits. You cannot request a limit increase for these
limits.

T3 Instances

If you plan to use your T3 Spot Instances immediately and for a short duration, with
no
idle time for accruing CPU credits, we recommend that you launch your T3 Spot
Instances in
standard mode to avoid paying higher costs.

If you launch your T3 Spot Instances in unlimited mode and burst CPU immediately, you'll spend
surplus credits for bursting. If you use the instance for a short duration, your
instance doesn't have time to accrue CPU credits to pay down the surplus credits,
and you are charged for the surplus credits when you terminate your instance.

Unlimited mode for T3 Spot Instances is suitable only if the instance runs for
long enough to accrue CPU credits for bursting. Otherwise, paying for surplus
credits makes T3 Spot Instances more expensive than M5 or C5 instances.

T2 Instances

Launch credits are meant to provide a productive initial launch experience for T2
instances by providing sufficient compute resources to configure the instance.
Repeated launches of T2 instances to access new launch credits is not permitted.
If
you require sustained CPU, you can earn credits (by idling over some period),
use
T2
Unlimited, or use an instance type with dedicated CPU (for example,
c4.large).

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